Various systems and methods for facilitating gas exchange with a fluid have been described in the literature. One application of such systems and methods are for use in lung assist technologies, which supplement the function of a damaged lung in a patient. Another application of such systems and methods are for use in industrial processes where it is desirable to exchange gas in fluid.
Certain systems and methods described previously facilitate gas exchange with a fluid using hollow fiber membranes and/or thin sheet membranes. Generally, hollow fiber membranes are thin-walled, gas-permeable hollow fibers, which permit gas exchange between gas in the core of the fiber and fluid (e.g., blood) surrounding the fiber. A hollow fiber device typically includes a bundle of hollow fibers that is connected to a gas inlet and outlet. The fibers may be enclosed in a housing, which may be connected to a blood inlet and outlet. Blood flow is typically transverse the axis of the fibers.
Systems and methods that utilize a thin-sheet membrane to facilitate gas exchange generally have a thin sheet of gas permeable material separating a fluid chamber (e.g., a chamber for blood) from a gas chamber. Gas exchange occurs across the membrane between the two chambers, and the membrane and chambers can be rolled or folded to create a convenient form factor. The entire membrane and chambers can be enclosed within a housing that provides blood and gas inlets and outlets.
Systems for gas exchange utilizing a hollow fiber membrane and/or thin sheet membrane feature several disadvantages. First, hollow fiber membranes often have geometrically limited surface-to-volume ratios and limited control of blood flow patterns. For example, a round cross section geometry and fiber packing density of hollow fiber membranes limits the surface-to-volume ratio, thereby creating a performance limit. Second, the fiber packing geometry often does not allow for a tight control of the blood flow path, nor does it allow for precision engineering to mimic human vascular physiology. Since the blood flow path influences shear stress and other blood flow characteristics that impact blood health, hollow fiber membranes generally do not provide a means to control or limit damage to patient blood. For their part, thin sheet membranes often have limited gas transfer due to, for example, blood side boundary layer conditions, restrictions on blood chamber height, and blood and gas chamber configurations that limit gas exchange to two directions. In addition, thin sheet membranes are often fairly thick, having for example, a thickness of at least 75 μm, since the membranes may be unsupported in certain areas.
Accordingly, a need exists for improved systems and methods of exchanging gas in a microfluidic device. The present invention addresses this need and provides other related advantages.